This invention relates to a device especially suited for, but not limited to, use as an attachment to a weight stack type exercise machine, for generating greater exercise resistance when the weight stack is moving in one direction (corresponding to eccentric muscle movements) than when the stack is moving in the opposite direction (corresponding to concentric muscle movements).
Weight stack type exercise machines have a stack of weights with a pin or other device to connect a selected number of the weights to one end of a lifting cable, the other end of the lifting cable being connected through one or more pulleys to a handlebar, pivotally mounted leg bar, or other movable member for engaging part of the body. Large numbers of such machines are currently in use.
Such conventional weight stack type exercise machines require the user exert the same amount of force to gradually lift the weight stack as to gradually lower the weight stack. During the weight stack lifting phase of an exercise the muscles involved contract or shorten, involving concentric muscle movements; whereas during the weight stack lowering phase the muscles involved lengthen, involving eccentric muscle movements.
Therefore such conventional weight stack type exercise machines are limited to presenting the same resistance to eccentric muscle movements as to concentric muscle movements.
However, muscles can generate significantly greater force during eccentric (muscle lengthening) exercise motions than during concentric (muscle shortening) exercise motions.
This difference between concentric and eccentric movements has been recognized, and various approaches have been taken to provide increased resistance during eccentric movements.
In one approach athletes work out in pairs on weight stack type and other exercise machines, or simply by lifting weights without a machine. The person who is exercising raises and lowers the weights. The second person either assists during the concentric phase or presses down on the weight to add force during the eccentric phase.
Machines are known in the art which are capable of applying greater forces during eccentric movements than the forces applied during the opposite, or concentric movements. Such machines are relatively complex and expensive, and have not been well accepted.
In FIGS. 5 and 6 of U.S. Pat. No. 5,011,142 to Eckler entitled Exercise Control System, a weight stack 88 is supported by a piston rod 76 of a pneumatic cylinder 92, the piston rod being connected to a double acting piston 90 within the cylinder. A bidirectional valve 60 controls the air pressure supplied to the upper and lower surfaces of the piston 90, to add or subtract resistance to the exerciser's effort to raise or lower the weight stack 88. This arrangement, however, is unduly mechanically complex and limited by piston stroke length; and cannot readily be incorporated in existing weight stack type exercise machines.
U.S. Pat. No. 5,015,926 to Casler, entitled Electronically Controlled Force Application Mechanism For Exercise Machines, does not utilize a weight stack, but rather employs a continuously running DC motor, the motor being coupled to an exercise member via a variable torque magnetic particle clutch controlled by a microprocessor to vary the exercise resistance in response to the exercise force, speed and direction of motion. This system is mechanically complex and not suited for incorporation in existing weight stack type exercise machines.
U.S. Pat. No. 4,765,613 to Voris, entitled Progressive Resistance Exercise Device, provides progressively increasing exercise resistance in the (concentric) exercise direction, while reducing the resistance to zero in the opposite (eccentric) direction.
U.S. Pat. No. 5,117,170 to Keane et al., entitled Motor Control Circuit For A Simulated Weight Stack, employs a DC motor to simulate a weight stack, providing exercise resistance which is electrically controllable.
U.S. Pat. No. 5,133,545 to Moschetti et al., entitled Progressive Accommodating Resistance Exercise Device, has cables which can be pulled by the user in order to exercise. FIG. 6 of this reference shows a drum 158 around which is wound a cable 162, with a governor and friction brake mechanism for varying the resistance presented to rotation of the drum as the cable winds on or unwinds from the drum. The faster the cable is pulled, the faster the governor spins and the harder it presses on the brake.
Other references of interest are:
______________________________________ U.S. Pat. No. Inventor Title ______________________________________ 3,912,261 Lambert, Sr. Exercise Machine 4,511,137 Jones Compound Weight Lifting Exercising Machine 4,609,189 Brasher Operator Controlled Variable Force Exercis- ing Machine 4,623,146 Jackson Exercise Machine 4,650,185 Cartwright Exercise Machine With Improved Load Varying Arrangement 4,846,466 Stima, III Microprocessor Control- led Electro-Hydraulic Exercise System 5,037,089 Spagnuolo Exercise Device Having et al. Variable Resistance Capability 5,106,081 Webb Leg Exercise Machine 3,869,121 Flavell Proportioned Resistance Exercise Servo System 4,261,562 Flavell Electromagnetically Regulated Exerciser ______________________________________
None of the aforementioned references is capable of, or suitable for installation on existing weight stack type exercise equipment at reasonable cost without limiting the range of movement of the weight, so as to provide eccentric resistance which is adjustably greater than the concentric resistance of the equipment.
Accordingly, an object of the present invention is to provide apparatus suitable for use as an attachment to a weight stack type exercise machine, for generating greater exercise resistance in one direction (corresponding to eccentric muscle movements) than in the opposite direction (corresponding to concentric muscle movements).